For example, here are several mystery parts made of 6061 alloy aluminum for an engineer who wishes to remain anonymous.
From ka-t.org, a thin (0.063") aluminum 6061 gasket for an automotive application.
A piece of aluminum 0.25" (1/4") thick:
A closeup of the above piece, showing the surface quality of waterjet cut aluminum.
Several parts of a gearbox for a robot.
One of the parts from above, with a penny for scale reference: